U.S. patent number 4,782,477 [Application Number 06/903,487] was granted by the patent office on 1988-11-01 for optical recording medium with fluorine resin adhesive.
This patent grant is currently assigned to Kabushiki Kaisha Toshiba. Invention is credited to Akio Hori, Katsutarou Ichihara, Yoshiaki Terashima, Nobuaki Yasuda.
United States Patent |
4,782,477 |
Ichihara , et al. |
November 1, 1988 |
Optical recording medium with fluorine resin adhesive
Abstract
A magneto-optical recording disk has a transparent resinous
substrate with a pre-groove, and a metallic recording layer formed
above the substrate. A transparent adhesive layer is provided
between the substrate and the recording layer, for allowing a laser
beam to pass therethrough, and for causing the recording layer to
be tightly adhered to the substrate to thereby prevent the
recording layer from being peeled off from the substrate. The
adhesive layer is comprised of a fluorine resin material.
Inventors: |
Ichihara; Katsutarou (Tokyo,
JP), Terashima; Yoshiaki (Yokosuka, JP),
Yasuda; Nobuaki (Zushi, JP), Hori; Akio
(Kawasaki, JP) |
Assignee: |
Kabushiki Kaisha Toshiba
(Kawasaki, JP)
|
Family
ID: |
26387507 |
Appl.
No.: |
06/903,487 |
Filed: |
September 4, 1986 |
Foreign Application Priority Data
|
|
|
|
|
Sep 30, 1985 [JP] |
|
|
60-214519 |
Mar 6, 1986 [JP] |
|
|
61-47338 |
|
Current U.S.
Class: |
369/275.5;
346/135.1; 347/264; 369/13.35; 369/275.1; 369/284; 369/286;
369/288; 430/945; 524/844; G9B/11.047; G9B/7.139 |
Current CPC
Class: |
G11B
7/24 (20130101); G11B 11/10582 (20130101); Y10S
430/146 (20130101) |
Current International
Class: |
G11B
11/00 (20060101); G11B 11/105 (20060101); G11B
7/24 (20060101); G11B 007/24 (); G11B 011/12 () |
Field of
Search: |
;369/13,275,284,286,288
;430/945 ;427/412.5 ;428/63,64,65,62,40,43 ;423/301 ;346/135.1,76L
;524/544,545,546 ;156/333 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
0123223 |
|
Oct 1984 |
|
EP |
|
0139474 |
|
May 1985 |
|
EP |
|
0161807 |
|
Nov 1985 |
|
EP |
|
2497994 |
|
Jul 1982 |
|
FR |
|
47-34747 |
|
Sep 1974 |
|
JP |
|
59-65950 |
|
Apr 1984 |
|
JP |
|
60-79543 |
|
Jul 1985 |
|
JP |
|
61-32238 |
|
Feb 1986 |
|
JP |
|
61-32237 |
|
Feb 1986 |
|
JP |
|
61-292239 |
|
Dec 1986 |
|
JP |
|
0711096 |
|
Jan 1980 |
|
SU |
|
1391610 |
|
Apr 1975 |
|
GB |
|
Other References
Patents Abstracts of Japan, vol. 8, No. 208, (P-302) [1645], Sep.
21, 1984. .
Patents Abstracts of Japan, vol. 10, No. 60, (P-435) [2117], Mar.
11, 1986. .
Patents Abstracts of Japan, vol. 8, No. 204, (p-301), 9/18/84.
.
Patents Abstracts of Japan, vol. 9, No. 109, (p-355), 5/14/85.
.
Topical Meeting on Optical Data Storage, Washington, D.C., pp.
TUAA3-1-TUAA3-4, K. Taira et al., 15-17 Oct. 1985, "Magneto-Optic
Erasable Disc Memory With Two Optical Heads"..
|
Primary Examiner: Cardillo; Raymond F.
Assistant Examiner: Nguyen; Hoa T.
Attorney, Agent or Firm: Oblon, Fisher, Spivak, McClelland
& Maier
Claims
What is claimed is:
1. An optical recording medium comprising:
a transparent resinous substrate with a pre-groove, said substrate
allowing a radiation beam to pass therethrough;
a metallic recording layer formed above said substrate, said
recording layer changing its optical characteristic in an area on
which the radiation beam is focused to form a beam spot; and
a transparent adhesive layer provided between said substrate and
said recording layer, for allowing the radiation beam to pass
therethrough, and for causing said recording layer to be adhered to
said substrate to prevent said recording layer from being peeled
off from said substrate, said adhesive layer comprising a fluorine
resin material which is contained therein in such a manner that
said adhesive layer is made of pure fluorine resin material at
least in the surface region of said adhesive layer which is in
contact with said substrate, to thereby maximize the adhesion force
between said transparent resinous substrate and said metallic
recording layer.
2. The recording medium according to claim 1, wherein said adhesive
layer comprises a transparent inorganic layer which is dielectric
and in which a fluorine resin component is contained.
3. The recording medium according to claim 2, wherein said fluorine
resin component is contained in said transparent inorganic layer in
such a manner that a composition ratio of said fluorine resin
component is varied along a perpendicular direction thereof.
4. The recording medium according to claim 3, wherein said fluroine
resin component is distributed in said transparent inorganic layer
in a manner that the composition ratio of said fluorine resin
component is larger than an averaged value of the composition ratio
of said fluorine resin component in a first interface region
between said substrate and said adhesive layer, said composition
ratio of said fluorine resin component being smaller than said
averaged value in a second interface region between said adhesive
layer and said recording layer.
5. The recording medium according to claim 4, wherein the
composition ratio of said fluorine resin component is continuously
varied in said transparent inorganic layer along the perpendicular
direction thereof.
6. The recording medium according to claim 4, wherein the
composition ratio of said fluorine resin component is
discontinuously varied in said transparent inorganic layer along
the perpendicular direction thereof.
7. The recording medium according to claim 4, wherein the
composition ratio of said fluorine resin component is set to be
substantially zero in said second interface region of said
transparent inorganic layer.
8. The recording medium according to claim 5, wherein the
composition ratio of said fluorine resin component is set to be
substantially zero in said second interface region of said
transparent inorganic layer.
9. The recording medium according to claim 6, wherein the
composition ratio of said fluorine resin component is set to be
substantially zero in said second interface region of said
transparent inorganic layer.
10. The recording medium according to claim 4, wherein said
recording layer comprises a magneto-optical recording layer.
11. The recording medium according to claim 1, further
comprising:
first and second protective layers provided to sandwich said
recording layer, for protecting said recording layer from being
oxidized, said recording layer comprising a magneto-optical
recording layer of rare-earth-transition metal amorphous
ferrimagnetic alloy.
12. The recording medium according to claim 11, wherein said
protective layers comprise inorganic dielectric layers which are
transparent to allow the radiation beam to pass therethrough.
13. The recording medium according to claim 12, wherein said
fluorine resin component is included in said transparent inorganic
layer at a constant composition ratio.
14. The recording medium according to claim 12, wherein said
transparent inorganic layer is made of fluorine resin material.
15. The recording medium according to claim 12, wherein said
adhesive layer comprises a transparent inorganic layer which is
dielectric and in which a fluorine resin component is
contained.
16. The recording medium according to claim 15, wherein said
fluorine resin component is contained in said transparent inorganic
layer in such a manner that a composition ratio of said fluorine
resin component is varied along a perpendicular direction
thereof.
17. The recording medium according to claim 16, wherein said
fluorine resin is distributed in said transparent inorganic layer
in a manner that the composition ratio of said fluorine resin
component is larger than an averaged value of the composition ratio
of said fluorine resin component in a first interface region
between said substrate and said adhesive layer, said composition
ratio of said fluorine resin component being smaller than said
averaged value in a second interface region between said adhesive
layer and said first protective layer.
18. The recording medium according to claim 17, wherein the
composition ratio of said fluorine resin component is continuously
varied in said transparent inorganic layer along the perpendicular
direction thereof.
19. The recording medium according to claim 17, wherein the
composition ratio of said fluorine resin component is
discontinuously varied in said transparent inorganic layer along
the perpendicular direction thereof.
Description
BACKGROUND OF THE INVENTION
The present invention relates to optical recording media and in
particular, to a magneto-optical recording medium having a
recording layer formed on a transparent resin substrate through
which a light beam is introduced to the recording layer.
Recently, considerable effort has been given to the development of
optical recording media. Such recording media offer an advantage
over conventional magnetic tapes or disks in that they can store
data information at high recording density to provide very large
storage capabilities.
A disk-shaped optical recording disk of the type known as an
optical disk or diskette can include a metallic recording layer
which is formed on a transparent substrate with a pre-groove. The
substrate requires a minimum birefringence to reduce the noise
level of a light signal, as well as its transparency for light beam
transmission. In order to meet such requirements and allow easy
formation of the pre-groove in the substrate, a transparent resin
material (e.g., polymethyl methacrylate, polycarbonate, epoxy, and
the like) is preferred as the substrate material.
The above transparent resin material, however, has poor adhesive
properties with a metal or metallic compound constituting a
recording layer. Therefore, it is difficult to form a metallic
recording layer on the transparent resin substrate. This is a
serious obstacle to practical application of an optical disk. In
particular, in a magneto-optical disk as one of the most promising
optical recording media, this problem is more serious. This is
since a magneto-optical disk adopts a rare earth-transision metal
amorphous ferrimagnetic film (to be referred to as an "RE-TM film"
hereinafter) as a recording layer, and the RE-TM film has poor
adhesive properties with respect to the resin substrate. This
problem is most urgent in the development of magneto-optical
disks.
In order to solve the above problem, according to Japanese Patent
Disclosure (KOKAI) No. 60-79543, an adhesive layer consisting of a
polymer layer is formed between the recording layer and the
transparent resin substrate to adhere them. The adhesive layer is
deposited on the substrate with a pre-groove by a spin-coat method
using a wet process (formation of the pre-groove after that of the
adhesive layer is not practical in the manufacture of the optical
disk).
However, if the wet process is adopted, it becomes very difficult
to uniformly deposit the adhesive layer on the entire surface of
the substrate having the pregroove. The thickness of the adhesive
layer varies widely on the wall portions of the pre-groove, and
becomes nonuniform on the bottom portion thereof. As a result, the
deposited adhesive layer cannot satisfactorily transform a
sectional shape of the pre-groove. Therefore, the pre-groove
defined on the adhesive layer is deformed, thus degrading
fundamental data read/write control characteristics of the optical
disk (e.g., tracking, focusing, and random-access). In the proposed
optical disk with the pre-groove, if the adhesive properties
between the recording layer and the substrate are to be improved,
this may degrade fundamental characteristics of the disk. Thus, the
optical disk proposed in the above disclosure is not the solution
to the above problem.
SUMMARY OF THE INVENTION
It is therefore an object of the present invention to provide a new
and improved optical recording medium with a pre-groove in which a
recording layer can be tightly adhered to a substrate without
degrading fundamental optical characteristics thereof.
In accordance with the above object, the present invention is
addressed to a specific recording medium which includes a resinous
substrate with a pre-groove. The substrate is transparent so as to
allow a radiation beam to pass therethrough. Above the substrate a
metallic recording layer is formed which changes its optical
characteristic in an area onto which the radiation beam is focused,
to thereby store binary data. A transparent adhesive layer is
provided between the substrate and the recording layer, for
allowing the radiation beam to pass therethrough. The adhesive
layer adheres the recording layer to the substrate to prevent the
recording layer from being peeled off therefrom. The adhesive layer
comprises a fluorine resin material, which can be formed by a known
dry process formation, such as sputtering or plasma polymerization.
Using these film formation techniques, the adhesive layer can be
uniformly disposed on the substrate with the pre-groove, so that
the recess shape of the pre-groove can be well inherited
(succeeded) to the adhesive layer to prevent the degradation of
tracking control of the optical disk due to the formation of the
adhesive layer.
The invention, and its objects and advantages, will become more
apparent in the detailed description of preferred embodiments
presented below.
BRIEF DESCRIPTION OF THE DRAWINGS
In the detailed description of a preferred embodiment of the
invention presented below, reference is made to the accompanying
drawings in which:
FIG. 1 shows a sectional view of a disk-shaped magneto-optical
recording medium having an adhesive layer provided between a
substrate and a recording layer in accordance with one preferred
embodiment of the invention not drawn to scale;
FIG. 2 shows a sputtering apparatus used for forming a
multi-layered structure of the recording layer and the adhesive
layer on the substrate in the production of the magneto-optical
recording medium of FIG. 1 and drawn to an enlarged scale;
FIGS. 3A and 3B are photomicrographs showing the structural
compositions of metal surface of magneto-optical recording disks
after the performance of an accelerated degradation test, the
magneto-optical recording disks each having a transparent adhesive
layer made by a sputtering method;
FIG. 4 shows a plasma polymerization apparatus used for forming the
adhesive layer on the substrate in another example of the
production of the magneto-optical recording medium of FIG. 1 and
drawn to an enlarged scale;
FIGS. 5A and 5B are graphs showing the variations of the
composition ratio of fluoroethylene in the transparent adhesive
layer of the magneto-optical recording disk, along the
perpendicular direction to the layer surface;
FIGS. 6A and 6B are photomicrographs showing the structural
compositions of metal surface of magneto-optical recording disks
after the performance of an accelerated degradation test, the
magneto-optical recording disks each having a transparent adhesive
layer in which the composition ratio of tetrafluoroethylene is
varied along a perpendicular direction to the layer surface;
FIGS. 7A and 7B are photomicrographs showing the structural
compositions of metal surface of magneto-optical recording disks
after the performance of an accelerated degradation test, the
magneto-optical recording disks each having a transparent adhesive
layer in which fluoroethylene is uniformly contained; and
FIG. 8 shows a sectional view of a disk-shaped magneto-optical
recording medium having an adhesive layer provided between a
substrate and a recording layer in accordance with another
embodiment of the invention not drawn to scale.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
There is shown in FIG. 1 of the drawings a data-erasable
disk-shaped magneto-optical recording medium, which is designated
generally by the numeral 10. This recording medium (referred to as
"magneto-optical disk" or "optical disk" hereinafter) 10 has a
transparent resinous substrate 12 on which is formed a guide groove
14 known as "pre-groove" among those skilled in the art. The
pre-groove 14 may be a plurality of concentric grooves or a spiral
groove. Substrate 12 comprises a transparent resin material (e.g.,
polycarbonate) to allow data read/write radiation beam 16
(indicated by the wavy arrow in FIG. 1) to pass therethrough.
Substrate 12 can also comprise a transparent resin material such as
polymethyl methacrylate, epoxy, or the like.
Adhesive layer 18 and recording layer 20, which is made of a rare
earth-transition metal amorphous ferrimagnetic alloy thin film
(RE-TM film), are sequentially deposited on the surface of
substrate 12 on which pregroove 14 is formed. In this embodiment,
recording layer 20 comprises, e.g., a terbium-cobalt (Tb-Co) film,
and adhesive layer 18 comprises a transparent insulative layer
containing a fluorine resin. Since adhesive layer 18 is also
transparent as is substrate 12, data read/write beam 16 passes
through substrate 12 and adhesive layer 18, and is guided to Tb-Co
recording layer 20.
Although the composition ratio of the fluorine resin in adhesive
layer 18 can be uniform in its entire region, it is more preferable
that the composition ratio is increased gradually or stepwise from
Tb-Co recording layer 20 toward substrate 12. In this case, if an
average composition ratio in the entire region of layer 18 is given
by x', composition ratio x of the fluorine resin component in
adhesive layer 18 varies along the direction of thickness of layer
18 to satisfy the following relation:
(1) in the interface region with substrate 12
x>x'
(2) in the interface region with layer 20
x<x'
When the fluorine resin component is distributed in adhesive layer
18 to satisfy the above relations, a peel-off prevention effect of
recording layer 20 from substrate 12 can be enhanced. In this way,
upon control of the distribution of the fluorine resin component,
the reliability of an optical disk under severe environmental
conditions (e.g., high temperature and high humidity) can be
improved.
Interference layer 22 and light reflection layer 24 are
sequentially formed on Tb-Co recording layer 20. Interference layer
22 comprises an insulative layer (e.g., Si.sub.3 N.sub.4), and
light reflection layer 24 comprises a metal layer (e.g., aluminum).
Laser beam 16 radiated onto recording layer 20 through substrate 12
and adhesive layer 18 is effectively reflected by reflection layer
24.
FIG. 2 shows a schematic arrangement of a sputtering apparatus used
when the optical disk having the multi-layered structure is
manufactured. Sputter chamber 30 has a plurality of, e.g., four,
magnetron sputter sources 32 therein. FIG. 2 illustrates only two
sputter sources 32L and 32R for the sake of simplicity. The
suffixes L and R stand for left and right and will be used for
other elements as well. Where it is not necessary to distinguish
between left and right, the suffixes may be dropped. Sputter
sources 32L and 32R are arranged on the bottom portion of sputter
chamber 30, and are respectively connected to RF power supplies 34L
and 34R, arranged outside chamber 30. Shutters 36L and 36R can be
opened or closed so as to cover sputter sources 32L and 32R,
respectively.
Sputter chamber 30 has sputter gas supply port 38 and sputter gas
exhaust port 40 in its wall portion. Ports 38 and 40 are
respectively coupled to sputter gas supply unit 42 and air exhaust
unit 44. Prior to sputtering, sputter chamber 30 is evacuated by
unit 44 to an appropriate vacuum. Thereafter, a sputter gas
necessary for sputtering is supplied to sputter chamber 30 by gas
supply unit 42.
Upper wall unit 46 is arranged on the upper portion of sputter
chamber 30 to be vertically movable. Upper wall unit 46 is
vertically moved by known elevator mechanism 48. When unit 46
reaches its lowermost position, it closes the upper opening of
sputter chamber 30, as shown in FIG. 2, thus sealing the internal
space of chamber 30 from its exterior. Sputter chamber 30 has a
table-like rotatable substrate holder 50. Substrate 12 of an
optical disk to be sputtered, is placed and fixed on the lower
surface of holder 50. Holder 50 is coupled to rotator 52 through a
rotating shaft, and is electrically connected to RF power supply
54. When substrate 12 of the optical disk to be sputtered is placed
on the lower surface of holder 50, upper wall unit 46 is driven
upward by elevator 48, and the substrate is mounted while the upper
opening of sputter chamber 30 is kept open.
The present inventors prepared optical disks having the fundamental
multi-layered structure shown in FIG. 1 using the sputtering
apparatus shown in FIG. 2. Four examples will be described
below.
EXAMPLE 1
An optical disk having the structure in FIG. 1 was produced using
the sputtering apparatus shown in FIG. 2 in the following manner. A
polycarbonate substrate with a pre-groove having a diameter of 120
mm and a thickness of 1.2 mm was used as transparent resin
substrate 12. First, a stamper was prepared from a master disk
obtained by exposing and developing a photopolymer by an Ar-ion
laser, and then a polycarbonate resin was injection-molded using
the stamper. Substrate 12 obtained was subjected to ultrasonic
cleaning in a neutral detergent solution for 5 minutes, and was
then washed with pure water. After N.sub.2 blow drying and
desiccator drying, the substrate was placed into sputter chamber 30
and was fixed to holder 50 by screws, as shown in FIG. 2. Elevator
48 was driven to move unit 46 downward, thus sealing sputter
chamber 30. Thereafter, exhaust unit 44 was driven to evacuate
sputter chamber 30 to a pressure of 5.times.10.sup.-6 Torr, and
99.999% purity Ar gas was supplied to chamber 30 from gas supply
unit 42, thus maintaining the gas pressure in chamber 30 at
5.times.10.sup.-3 Torr. Next, holder 50 was rotated at 60 rpm by
rotator 52, and 150-W RF power was applied to sputter source 32L
(which stored a 5-inch tetrafluoroethylene target) from power
supply 34L while one (36L) of shutters 36 was closed. Pre-sputter
(sputter with one closed shutter 36) was performed for 5 minutes to
clean the target surface. Thereafter, shutter 36L was opened and
sputter film formation was performed for about 20 minutes. Then,
power supply 34L was turned off, and sputter chamber 30 was
released to the outer atmosphere. Unit 46 was moved upward by
elevator 48 and substrate 12, on which adhesive layer 18 comprising
fluoroethylene was formed, was removed from chamber 30. Using
glass, polymethyl methacrylate, polycarbonate, and epoxy samples
(about 15 mm.times.25 mm) placed on holder 50 at the same time, the
film qualities of adhesive layers formed by the above method were
evaluated. As a result, the film thickness was 100 nm, a
transmittance was 93% (wavelength 830 nm, polymethyl methacrylate
substrate), and a chemical resistance was high such that no change
in properties was found after a 30-min acetone ultrasonic cleaning.
The adhesive property of the adhesive layer with respect to the
substrate was strong such that no film was peeled off from any of
the polymethyl methacrylate, polycarbonate, epoxy, and glass
substrates in a peel-off test using an adhesive tape. In addition,
after four cycles of accelerated degradation tests, each cycle
including 24-Hr. aging under high-temperature, high-humidity
atmosphere (at a temperature of 65.degree. C. and a humidity of
90%R.H.) and 1-Hr. aging under ambient atmosphere, the resultant
adhesive layer was not peeled off from any of the above four
substrates, and no change in properties (e.g., a change in
transmittance) of the fluoroethylene film itself was found.
As Comparative Example 1, an Si.sub.3 N.sub.4 underlying layer was
formed in place of adhesive layer 18. N.sub.2 -Ar gas mixture
containing N.sub.2 at 3% partial pressure was used as the sputter
gas, RF power applied to an Si target was 300 W, and a film
formation duration was 20 minutes. When the thus obtained Si.sub.3
N.sub.4 underlying layer was evaluated in the same manner as the
adhesive layer of the fluoroethylene film, the film thickness was
100 nm, the transmittance was 91%, and no changes in properties was
found after 30-min acetone ultrasonic cleaning. As for the adhesive
property with respect to the substrate, the layer was not peeled
off when it was formed on the glass substrate, and it was easily
peeled off from the polymethacrylate, polyimide, or epoxy resin
substrate. After four cycles of the same accelerated degradation
tests as above, no peel-off of the Si.sub.3 N.sub.4 underlying
layer was found, only when it was formed on the glass substrate,
and Si.sub.3 N.sub.4 layers formed on the other resin substrates
were locally peeled off therefrom (10-.mu.m wide wrinkles were
formed), resulting in degradation in transmittance.
Next, Si, Tb, Co, and Al targets were arranged in four sputter
sources 32 shown in FIG. 2, and recording layer 20 of a Tb-Co film,
interference layer 22 of an Si.sub.3 N.sub.4 film, light reflection
layer 24 of an Al film were formed with the same batch on a
polycarbonate substrate on which adhesive layer 18 was formed and
on a polycarbonate substrate on which the Si.sub.3 N.sub.4
underlying layer as Comparative Example was formed. Each of these
two substrates was fixed to holder 50 by screws in sputtering
apparatus shown in FIG. 2, and unit 46 was moved downward. Sputter
chamber 30 was evacuated to 5.times.10.sup.-6 Torr by exhaust unit
44, and 99.999% purity Ar gas was supplied in chamber 30 by gas
supply unit 42, thus maintaining the gas pressure in chamber 30 at
5.times.10.sup.-5 Torr. Thereafter, RF power supply 54 was turned
on to apply 300-W RF power, so that the substrate surface was
subjected to 5-min sputter etching processing. Then, the substrates
were cleaned.
Next, shutters 36 corresponding to Tb-target and Co-target sputter
sources 32 were closed. In this state, pre-sputter was performed
for 5 minutes such that DC power was applied to sputter sources 32
from RF power supplies 34, so that discharge currents of 0.5 A and
1.5 A flowed through the Tb and Co targets, respectively, thereby
cleaning the target surfaces. Thereafter, holder 50 was rotated at
60 rpm by rotator 52. Shutters 36 corresponding to Tb-target and
Co-target sputter sources 32 were simultaneously opened, and Tb-Co
film formation was performed for 35 seconds. As a result, recording
layer 20 comprising a 35-nm thick Tb-Co film was formed on each
substrate. Thereafter, power supplies 34 were turned off.
Next, the sputter gas was changed to a N.sub.2 -Ar gas mixture
containing N.sub.2 at 3% partial pressure, and 300-W RF power was
applied to Si-target sputter source 32 from the corresponding power
supply 34, thereby performing pre-sputter for 5 minutes. After
5-min sputter film formation, interference layer 22 comprising a
25-nm thick Si.sub.3 N.sub.4 layer was formed on recording layer
20.
Next, the sputter gas was changed to pure Ar gas, and 300-W RF
power was applied to Al-target sputter source 32 from corresponding
power supply 34, thus performing pre-sputter for 5 minutes. After a
10-min sputter film formation, light reflection film 24 comprising
a 100-nm thick Al film was formed on interference layer 22
comprising the Si.sub.3 N.sub.4 film. Thereafter, power supply 34
was turned off, and rotation of substrates 12 was stopped. Sputter
chamber 30 was released to ambient pressure, substrates 12 were
moved upward by unit 46, and the optical disks shown in FIG. 1 were
removed from chamber 30.
Meanwhile, using glass, polymethyl methacrylate, polycarbonate, and
epoxy samples each having the adhesive layer of a 100-nm
fluoroethylene film, and similar samples each having a 100-nm
Si.sub.3 N.sub.4 film, which were placed on holder 50 at the same
time, their characteristics immediately after film formation were
evaluated. More specifically, reflectivity R and Kerr rotation
angle .theta.k were measured by irradiating the substrate surfaces
with He-Ne laser beam. As a result, in the samples in which the
fluoroethylene adhesive layer was formed on the polymethyl
methacrylate substrate, R=20% and .theta.k=0.45 deg. In the samples
having the Si.sub.3 N.sub.4 film, R=25% and .theta.k=0.45 deg. In
the structure of the present invention having the fluoroethylene
adhesive layer, it was confirmed that a reproduction characteristic
index (product of R.times..theta.k) high enough for practical
applications could be obtained.
In the peel-off test using the adhesive tape, in the samples having
the fluoroethylene adhesive layer, no peel-off occurred in any of
glass, polymethyl methacrylate, polycarbonate, and epoxy
substrates. In contrast to this, in the samples having the Si.sub.3
N.sub.4 underlying layer, peel-off occurred except for the glass
substrate. These samples and an optical disk using a polycarbonate
substrate with a pre-groove having a diameter of 120 mm were
subjected to the accelerated degradation tests in which 24-Hr.
aging at a temperature of 65.degree. C. and a humidity of 90%R.H.,
1-Hr. aging at ambient temperature, and 48-Hr. aging at a
temperature of 65.degree. C. and a humidity of 90%R.H. were
repeated, thus examining the occurrence of peel-off. FIGS. 3A and
3B show photomicrographs of metal compositions showing the surface
conditions of the optical disk of the present invention after the
accelerated degradation test. FIG. 3A is a photomicrograph at a
magnification of 10 times, and FIG. 3B is a photomicrograph at a
magnification of 1,000 times. As can be seen from FIGS. 3A and 3B,
no peel-off occurred on both the surfaces with and without a
pre-groove (stripe portions). In contrast to this, in the
conventional optical disk having the Si.sub.3 N.sub.4 underlying
layer, the film was peeled off from the substrate during the
accelerated degradation test. As can also be seen from the
photomicrographs in FIGS. 3A and 3B, the shape of the pregroove
could be kept unchanged without deformation.
EXAMPLE 2
In Example 1, the fluoroethylene adhesive layer was formed by a
sputtering method. However, the fluoroethylene adhesive layer can
be obtained by a method wherein Freon gas is plasma-polymerized.
FIG. 4 shows a plasma polymerization apparatus applied to formation
of the fluoroethylene adhesive layer. Referring to FIG. 4,
reference numeral 60 denotes a polymerization chamber; and 62, a
substrate holder for holding resin substrate 12 (e.g., polymethyl
methacrylate substrate with a pregroove having a diameter of 120
mm). Reference numeral 64 denotes a coil; 66, an RF power supply;
68, a plasma gas supply unit; and 70, an exhaust unit.
Using the above plasma polymerization apparatus, a fluoroethylene
adhesive layer was formed in the following manner. First,
polymerization chamber 60 was evacuated to 5.times.10.sup.-8 Torr
by exhaust unit 70. Thereafter, 10 sccm of CF.sub.4 gas and 10 sccm
of Ar gas were simultaneously supplied to chamber 60 from gas
supply unit 68. RF power supply 66 was turned on, and 200-W RF
power was then applied to coil 64. CF.sub.4 -Ar gas mixture plasma
was excited in chamber 60, and plasma polymerization film formation
on substrate 12 was performed for 30 minutes. Thereafter, substrate
12 was removed from chamber 60. As for the film quality of the
resultant plasma polymerized fluoroethylene film, although the
chemical resistance was slightly lower than that of the sputter
fluoroethylene film, other properties were as good as those of the
sputter fluoroethylene film. A recording layer of a Tb-Co film, an
interference layer of an Si.sub.3 N.sub.4 film, and a light
reflection layer of an Al film were sequentially formed on the
plasma polymerized fluoroethylene film using the sputtering
apparatus shown in FIG. 2, and the resultant multilayer was
subjected to the accelerated degradation test as in Example 1. As a
result, no peel-off of the films occurred and no degradation in the
shape of the pre-groove was found.
EXAMPLE 3
In Examples 1 and 2, the adhesive layer was formed only of a
fluorine resin (fluoroethylene). The adhesive layer of the present
invention can contain an inorganic material having a transparency
in addition to the fluorine resin.
As transparent resin substrate 12, the same polycarbonate substrate
with a pre-groove as in Example 1 was prepared. The substrate was
subjected to ultrasonic cleaning in a neutral detergent solution
for 5 minutes, and was washed with pure water. Thereafter, N.sub.2
blow drying and desiccator drying were performed. The cleaned
substrate was fed into sputter chamber 30 of the sputtering
apparatus shown in FIG. 2, and was fixed to substrate holder 50 by
screws. Unit 46 was moved downward to seal sputter chamber 30.
Exhaust unit 44 was driven to evacuate sputter chamber 30 to
5.times.10.sup.-5 Torr. Thereafter, N.sub.2 -Ar gas mixture
containing N.sub.2 at 3% partial pressure was supplied to sputter
chamber 30 from gas supply unit 42 to maintain the gas pressure
inside chamber 30 at 5.times.10.sup.-3 Torr. Next, holders 50 was
rotated at 60 rpm, and 150-W RF power and 120-W RF power were
applied to sputter sources 32 (respectively storing 5-inch
tetrafluoroethylene and Si targets) from the corresponding power
supplies 34 while two shutters 36 above the corresponding sputter
sources 32 were closed. Pre-sputter (sputter with two shutters 36
closed) was performed for 5 minutes, thus cleaning the target
surfaces. Next, two shutters 36 were opened, and sputter film
formation was performed for about 10 minutes. Thereafter, power
supplies 34 were turned off, and sputter chamber 30 was released to
ambient pressure. Unit 46 was moved upward and substrate 12 on
which adhesive layer 18 comprising fluoroethylene 75 vol.
%-Si.sub.3 N.sub.4 25 vol. % was removed from chamber 30. Using
glass, polymethyl methacrylate, polycarbonate, and epoxy samples
(about 15 mm.times.25 mm) placed on holder 50 at the same time, the
film quality of adhesive layer 18 formed thereon was evaluated. As
a result, the film thickness was 100 nm, the transistance was 91%
(wavelength 830 nm, polymethyl methacrylate substrate), and the
chemical resistance was high such that no changes in properties
were found after a 30-min acetone ultrasonic cleaning. The adhesive
property of the adhesive layer with respect to the substrate was
also high such that no film was peeled from any of the polymethyl
methacrylate, polycarbonate, epoxy, and glass substrates in the
peel-off test using an adhesive tape. In addition, after four
cycles of accelerated degradation test, each cycle including 24-Hr.
aging under high-temperature, high-humidity atmosphere (at a
temperature of 65.degree. C. and a humidity of 90%R.H.) and 1-Hr.
aging under ambient atmosphere, no film was peeled off from any of
the four substrates, and no change in properties (e.g., a change in
transmittance) of the fluoroethylene film itself was found.
According to the present invention, if the adhesive layer comprises
a mixture of the fluorine resin and an inorganic material,
substantially the same effect as with the fluorine resin can be
obtained.
EXAMPLE 4
In Example 3, the adhesive layer comprising the mixture of
fluoroethylene and Si.sub.3 N.sub.4 has a constant composition
ratio of fluoroethylene (i.e., 75 vol. %). However, after the
repeated accelerated degradation tests for a long period of time
under severer conditions, the present inventors found that the
reliability could be improved when the composition ratio of the
fluorine resin varied along the direction of thickness of the
adhesive layer of this type. In this case, in order to reduce
differences in thermal expansion ratios and water absorption
expansion coefficients between the adhesive layer, the substrate
and the recording layer are as small as possible, composition ratio
x of the fluorine resin is varied so as to satisfy the following
relations:
at the substrate side, x>x'
at the recording layer side, x<x'
where x' is an average value of x along the direction of the
thickness.
FIGS. 5A and 5B are graphs when the composition ratio of the
fluorine resin is varied along the direction of thickness of the
adhesive layer, in which, FIG. 5A shows a case in which the
composition ratio is varied stepwise and FIG. 5B shows a case in
which the composition ratio varies gradually. The adhesive layers,
the composition ratios of which were varied as shown in FIGS. 5A
and 5B, could be formed by changing, over time, an input power
ratio to the tetrafluoroethylene target and the Si target in the
sputtering apparatus shown in FIG. 2. A recording layer of a Tb-Co
film, an interference layer of an Si.sub.3 N.sub.4 film, and a
light reflection layer of an Al film were sequentially formed on
these adhesive layers in the same manner as in Example 3 to prepare
optical disks. The optical disks were subjected to the accelerated
degradation test, together with the optical disk in Example 3
having the adhesive layer comprising the mixture of fluoroethylene
and Si.sub.3 N.sub.4 and having the constant composition ratio of
fluoroethylene (i.e., 75 vol. %), under severer conditions than
those of Example 3. In the test, four cycles of 24-Hr. aging at a
temperature of 80.degree. C. and a humidity of 90%R.H., 1-Hr aging
at ambient temperature, and 96-Hr. aging at a temperature of
80.degree. C. and a humidity of 90%H.R. were repeated.
FIGS. 6A and 6B and FIGS. 7A and 7B are photomicrographs of metal
textures showing the surface conditions of the optical disks after
the accelerated degradation test. FIG. 6A shows the surface
condition of the optical disk having the adhesive layer with a
stepwise change in composition ratio shown in FIG. 5A, FIG. 6B
shows the surface condition of the optical disk having the adhesive
layer with a gradual change in composition ratio shown in FIG. 5B,
and FIGS. 7A and 7B show the surface condition of the optical disk
having the adhesive layer, in which the composition ratio of
fluoroethylene is constant (i.e., 75 vol. %). FIGS. 6A and 6B and
FIG. 7A are photomicrographs at a magnification of 10 times, and
FIG. 7B is a photomicrograph at a magnification of 1,000 times.
The optical disk having the constant fluoroethylene composition
ratio exhibited no peel-off in the accelerated degradation test
performed under the conditions at a temperature of 65.degree. C.
and a humidity of 90%R.H. as in Example 3. However, as can be seen
from FIGS. 7A and 7B, stripe-like peel-off occurred locally in the
optical disk of Example 3 during the longer accelerated degradation
test at a temperature of 80.degree. C. and a humidity of 90%R.H. in
Example 4. The similar phenomenon was observed in the optical disk
in Example 1, in which the adhesive layer was comprised of only
fluoroethylene.
In contrast to this, in the optical disk having the adhesive layer
with the stepwise change in composition ratio, peel-off was found
only on a surface without the pre-groove, as shown in FIG. 6A. In
the optical disk having the adhesive layer having the gradual
change in composition ratio, no peel-off was found, as shown in
FIG. 6B. Therefore, a sufficiently high reliability can be expected
for the adhesive layer having the uniform composition ratio under
ambient atmosphere (e.g., in an office). However, if optical disks
need be stored under severe conditions for a long period of time,
the adhesive layer, in which the composition ratio of the fluorine
resin is varied along the direction of thickness of the adhesive
layer, can provide higher reliability.
When an adhesive layer having a stepwise change in composition
ratio shown in FIG. 5B and including a 100% fluoroethylene layer,
is to be formed, the 100% fluoroethylene layer can be formed by a
plasma polymerization method using CF.sub.4 gas. A layer of
fluoroethylene and an inorganic material can be formed by
simultaneously performing plasma polymerization using CF.sub.4 gas
and sputter of the inorganic material target. However, this
complicates manufacturing conditions. Therefore, simultaneous
sputter of the tetrafluoroethylene and inorganic material targets
is preferred.
According to the optical disk of the present invention described in
the above examples, transparent adhesive layer 18 comprising a
fluorine resin is provided between substrate 12 with pre-groove 14
and Tb-Co recording layer 20 in order to improve the adhesive
properties therebetween. Since adhesive layer 18 is transparent as
is substrate 12, it can improve the adhesive properties between
recording layer 20 and substrate 12 without degrading fundamental
optical characteristics of a magneto-optical recording disk, such
as a beam reflectance, Kerr hysteresis characteristics, and the
like, thus improving the reliability of the optical disk.
Since adhesive layer 18 can be formed by a dry process (e.g., a
sputtering method or a plasma polymerization method), it can be
uniformly deposited on substrate 12 to accurately reproduce the
small sectional shape of pre-groove 14 formed on substrate 12. The
small sectional shape of pre-groove 14 can be satisfactorily
duplicated by recording layer 20, and the fundamental data
read/write control characteristics (e.g., tracking, focusing,
rondom-access, and the like) of the optical disk with the
pre-groove can thus be improved.
Magneto-optical disk 100 according to another embodiment of the
present invention will now be described with reference to FIG. 8.
Referring to FIG. 8, laser beam 16 incident on the optical disk is
represented by the wavy arrow in the same manner as in FIG. 1.
Disk-shaped substrate 102 comprises a transparent resin material
(e.g., polycarbonate) in the same manner as in the previous
embodiment shown in FIG. 1, and has pre-groove 104. Transparent
adhesive layer 106 and transparent first protective layer 108-1 are
sequentially deposited on the surface of substrate 102 on which
pre-groove 104 is formed. Adhesive layer 106 comprises a
transparent insulative film containing a fluorine resin in the same
manner as in the previous embodiment. In this embodiment, adhesive
layer 106 contains fluoroethylene as the fluorine resin. First
protective layer 108-1 comprises a transparent inorganic
dielectric, e.g., Si.sub.3 N.sub.4.
Deposited on first protective layer 108-1 are recording layer 110
comprising a rare earth-transition metal amorphous ferrimagnetic
metal film such as a Tb-Co film, second protective layer 108-2, and
light reflection layer 112 comprising a metal film (e.g., an
aluminum film) having a high reflectivity. The composition of
second protective layer 108-2 is the same as that of first
protective layer 108-1. Tb-Co recording layer 110 is sandwiched
between first and second protective layers 108-1 and 108-2 in order
to prevent it from being oxidized since a magneto-optical recording
medium is very sensitive to oxidization. The optical disk having
the above structure can also be manufactured by a sputtering method
using the sputtering apparatus shown in FIG. 2, or by a plasma
polymerization method using the plasma polymerization apparatus
shown in FIG. 4.
It should be noted that adhesive layer 106 can comprise:
(1) a 100% fluorine resin (i.e., a resin material having C-F
bonds);
(2) a homogeneous mixture of a fluorine resin and an inorganic
dielectric; or
(3) a mixture of a fluorine resin and an inorganic dielectric, in
which the composition ratio of the fluorine resin in adhesive layer
106 increases gradually or stepwise from recording layer 110 toward
substrate 102 along the direction of thickness of adhesive layer
106.
Formation of such adhesive layer 106 can be realized by: (1)
sputtering a tetrafluoroethylene target; (2) simultaneously
sputtering a tetrafluoroethylene target and an inorganic dielectric
target; or (3) plasma-polymerizing Freon gas.
The present inventors manufactured optical disks having the
multi-layered structure shown in FIG. 8, using the sputtering
apparatus in FIG. 2. Some examples will be described below.
EXAMPLE 5
A magneto-optical recording disk having transparent adhesive layer
106 and first and second protective layers 108-1 and 108-2,
sandwiching recording layer 110 therebetween were manufactured in
basically the same manner as in Example 1. Transparent adhesive
layer 106 and recording layer 110 were formed in the same steps as
in Example 1.
After adhesive layer 106 was formed on substrate 102 with
pre-groove 104, Si, Tb, Co, and Al targets are placed in four
sputter sources 32 in FIG. 2. A polycarbonate substrate with
adhesive layer 106 and another polycarbonate substrate without
layer 106, as a comparative example, were fixed to substrate holder
50 in order to form thereon first protective layer 108-1 of an
Si.sub.3 N.sub.4 film film, recording layer 110 of a Tb-Co film,
second protective layer 108-2 of an Si.sub.3 N.sub.4 film, and
light reflection layer 112 of an Al film. Next, upper wall unit 46
was moved downward and sputter chamber 30 was evacuated to
5.times.10.sup.-6 Torr by exhaust unit 44. Thereafter, N.sub.2 -Ar
gas containing N.sub.2 at 3% partial pressure was supplied to
chamber 30 and the gas pressure in chamber 30 was maintained at
5.times.10.sup.-3 Torr. Then, 300-W RF power was applied to Si
target sputter source 32 from power supply 34, thus performing
pre-sputter (target cleaning while closing the corresponding
shutter 36) for 5 minutes. Next, the corresponding shutter 36 was
opened and formation of an Si.sub.3 N.sub.4 film was performed by
reactive sputtering for 20 minutes, thus forming a 100-nm thick
Si.sub.3 N.sub.4 film (corresponding to first protective layer
108-1) on adhesive layer 106 and substrate 102.
Next, sputter chamber 30 was again evacuated to 5.times.10.sup.-8
Torr by exhaust unit 44, and 99.999% purity Ar gas was supplied
thereto by gas supply unit 42, thus maintaining the gas pressure in
chamber 30 at 5.times.10.sup.-8 Torr. RF power supply 34 was turned
on so that the Si.sub.3 N.sub.4 film surface was cleaned by 5-min
sputter etching with 300-W RF power.
Next, DC power was applied to Tb and Co target sputter sources 32
while shutters 36 corresponding thereto were closed, so that 0.5-A
and 1.5-A discharge currents respectively flowed through Tb and Co
targets, thus performing 5-min pre-sputter. After the target
surfaces were cleaned, substrate holder 50 was rotated at 60 rpm by
rotator 52 and shutters 36 corresponding to sputter sources 32 were
simultaneously opened, thus forming a Tb-Co film for 35 seconds. As
a result, recording layer 110 of a 25-nm Tb-Co layer was formed,
and power supply 34 was then turned off.
Next, the sputter gas was changed to a N.sub.2 -Ar gas mixture
containing N.sub.2 at 3% partial pressure, and 300-W RF power was
applied to Si target sputter source 32 from corresponding power
supply 34, thus performing presputter for 5 minutes. Thereafter,
sputter film formation was performed for 5 minutes, thereby forming
a second protective layer 108-2 of a 25-nm thick Si.sub.3 N.sub.4
film on recording layer 110.
Next, the sputter gas was replaced with pure Ar gas, and 300-W RF
power was then applied to Al target sputter source 32 from power
supply 34, thus performing pre-sputter for 5 minutes. Thereafter,
sputter film formation was performed for 10 minutes, thus forming
light reflection layer 112 of a 100-nm thick Al film on protective
layer 108-2 of the Si.sub.3 N.sub.4 film. Power supply 34 was
turned off, the rotation of substrates 102 was stopped, and sputter
chamber 30 was then released to ambient pressure. Unit 46 was moved
upward and optical disks 100 shown in FIG. 8 was removed from
chamber 30.
Using glass, polymethyl methacrylate, polycarbonate, and epoxy
samples each having an adhesive layer comprising a 100-nm
fluoroethylene film and similar samples without an adhesive layer
as a comparative example, which were placed on holder 50 at the
same time, characteristics immediately after film formation were
evaluated. More specifically, reflectivity R and Kerr rotation
angle .theta.k were measured by irradiating substrate surface with
an He-Ne laser beam. As a result, the sample, having the
fluoroethylene adhesive layer on the polymethyl methacrylate
substrate, had R=20% and .theta.k=0.45 deg. The sample without the
adhesive layer had R=25% and .theta.k=0.45 deg. With the structure
of the present invention having the fluoroethylene adhesive layer,
a reproduction characteristic index (product of R.times..theta.k)
high enough for practical applications could be obtained.
In the peel-off test using an adhesive tape, no peel-off occurred
in any of the glass, polymethyl methacrylate, polycarbonate, and
epoxy substrates having the fluoroethylene adhesive layer. In
contrast to this, peel-off occurred in the samples having no
adhesive layer, except for the glass substrate. These samples and
the 120-mm optical disk with a pre-groove were subjected to the
accelerated degradation test, wherein 24-Hr. aging at a temperature
of 65.degree. C. and a humidity of 90%R.H., 1-Hr. aging at ambient
temperature, and 48-Hr. aging at a temperature of 65.degree. C. and
a humidity of 90%R.H. were repeated, and the occurrence of peel-off
was examined. FIGS. 3A and 3B show photomicrographs of metal
textures showing the surface conditions of the optical disk of the
present invention after the accelerated degradation test. FIG. 3A
is a photomicrograph at a magnification of 10 times, and FIG. 3B is
a photomicrograph at a magnification of 1,000 times. As can be seen
from FIGS. 3A and 3B, no peel-off occurred on both the surfaces
with and without a pre-groove (stripe portions). In contrast to
this, in the conventional optical disk having the Si.sub.3 N.sub.4
underlying layer, the film was peeled off from the substrate during
the accelerated degradation test.
EXAMPLE 6
A magneto-optical recording disk having first and second protective
layers 108-1 and 108-2 was prepared by a plasma polymerization
method using the apparatus shown in FIG. 4. In this case, first and
second protective layers 108-1 and 108-2 could be formed above
substrate 102 under substantially the same conditions as the film
formation conditions of Si.sub.3 N.sub.4 interference film in
Example 2.
According to the optical disk of the second embodiment of the
present invention as described above, the same effect as in first
embodiment can be obtained. In addition, with the optical disk of
the second embodiment, since protective layer 108-1 without
containing a fluorine resin component is provided between adhesive
layer 106 and recording layer 110, composition ratio x of the
fluorine resin need not be carefully controlled so as not to
contain the fluorine resin component in the interface region
between adhesive layer 106 and recording layer 110 in the first
embodiment (see FIG. 5A). This means that distribution control of
the fluorine resin component in adhesive layer 106 can be greatly
simplified, and contributes to simplify the manufacture of a
pre-groove optical disk having the adhesive layer.
Although the invention has been described with reference to
specific embodiments, it shall be understood by those skilled in
the art that numerous modifications may be made that are within the
spirit and scope of the inventive contribution.
For example, in the above embodiments, the recording layer
comprises a Tb-Co film having a magneto-optical effect, but can
comprise another RE-TM film. In addition, the adhesive layer of the
present invention can be applied to optical disks having recording
layers of, e.g., a CuAl film utilizing a shape memory effect, an
SeTe film utilizing a change in crystal structure, an InSb film,
and the like, and the same effect as in the previous embodiments
can be expected.
In the above embodiments, Si.sub.3 N.sub.4 is exemplified as a
transparent inorganic material mixed with a fluorine resin
(fluoroethylene). However, other inorganic materials, e.g.,
SiO.sub.2, SiO, AlN, ZnS, CaF.sub.2, ITO, and the like can be used
as well as Si.sub.3 N.sub.4, and the same effect can be obtained.
In a test, targets of these inorganic materials were subjected to
sputter together with a tetrafluoroethylene target to form adhesive
layers consisting of mixtures of these materials on polymethyl
methacrylate, polycarbonate, epoxy, and glass substrates, and the
resultant disks were subjected to a peel-off test as described
above. In the disks having the adhesive layer with uniform
fluoroethylene composition ratio of 50 vol. % or higher, no film
was peeled off from any type of substrate in which the
fluoroethylene composition layer was 50 vol. % or more, and no
peel-off was found in the adhesive layer having the gradual change
in composition ratio.
* * * * *